It takes a lot of eggs to make a whooping crane! If that sounds a bit bizarre, please bear with me; I can explain it.
It’s official that out in the fields and wetlands of Wisconsin – around Necedah National Wildlife Refuge – that nesting season is underway. One way or another, happy or sad, there will be news to share.
But for this post, I’m focusing on the eggs – and eventually the chicks – that will be produced by the captive populations of whooping cranes. There are five centers with captive breeding populations that are the source of all but seven of the cranes that have been released by the Whooping Crane Eastern Partnership (WCEP) into Wisconsin, since 2001, and Louisiana, since 2011. (The seven birds that did not hatch from eggs of the captive population, are cranes that have hatched in the wild in Wisconsin – exciting! But not nearly enough for the flock to survive on its own.)
By far, the majority of captive eggs for WCEP come from the population of whoopers at either the International Crane Foundation (ICF) here in Wisconsin, or Patuxent Wildlife Research Center in Maryland. The remaining sources of captive breeding whooping cranes are the Calgary Zoo in Alberta, Canada, the San Antonio Zoo in Texas, and the Audubon Center for Research on Endangered Species, in New Orleans.
Eggs Don’t Equal Chicks
One thing you can be sure of if you follow the production of eggs – ICF very helpfully posts an Egg Score Card with their news – the number of new little whooping crane chicks for 2015 will not equal the number of eggs produced. Not even close.
Last year, according to a report at Operation Migration, there were 106 eggs produced from captive breeding that were potentially available for the WCEP programs. Doesn’t that sound like it might be a bumper crop?
Well . . . not exactly. From that number only 25 chicks were available for WCEP to divide among the ultralight training program (7 chicks), the parent release program which was new in 2013 (4 chicks), and for the non-migratory flock that is being established in Louisiana (14 chicks). So here’s what happened to all those other eggs: a good many of them were infertile; some were broken by the cranes in their nests, and sometimes chicks that hatch do not survive.
Breeding Whooping Cranes at the International Crane Foundation
From the data provided by WCEP and its partners, I was getting the picture that probably more than half the eggs produced would never become whooping cranes. I needed help understanding this seemingly poor outcome, and Bryant Tarr, Curator of Birds at ICF, was happy to oblige.
“The numbers game with captive produced whooping cranes is always a bit of a guess,” he told me in an email last year. He added that breeding through artificial insemination – necessary “because we wish to control the genetics to avoid inbreeding in this tiny population” – makes the process even more of a guess. (He recently, reconfirmed for me that the info he shared a year ago is “all pretty much the same for this year.”)
Bryant said: “Natural fertility is usually higher. Fertility by artificial insemination usually results in about 50-60% fertile eggs in whooping cranes. And yes, some of the birds break their eggs. This likely happens more in captivity than in the wild and there may be many factors involved.” He suggested though, that wild nests are faced with the threat of predators, which of course are no threat to captive birds, “so there is kind of a wash going on there.”
Bryant added that about 40 fertile eggs were expected from the entire captive flock, but “40 fertile eggs does not equal 40 chicks for release!” he assured me. “You have to figure in ‘hatchability’ the percent of fertile eggs that hatch ( usually close to 80%) and survival after hatch (some young ones just don’t make it) and that is usually about 80% too.”
Count the Eggs and Do the Math
Applying Bryant’s percentages to last year’s count of 106 eggs reveals that the 25 whooping crane chicks that resulted were right on the mark. After accounting for 49 infertile eggs, and 19 broken ones, there were 38 potential eggs from the captive populations in 2014. Figuring that only about 80 percent of them actually hatched, and that only 80 percent of those hatchlings would survive for release, it’s true that approximately two dozen little whooping crane chicks is exactly what you would expect.
Stay tuned for news of this year’s egg totals and the whooper chicks that hatch for 2015. Egg and chicks season is underway, and at ICF the Egg Scorecard is currently reporting that eight eggs, so far, have been laid by the whooper population in residence there. It is too soon to know if 4 of them are fertile. But here are the relevant details on the other four: 2 have been identified as infertile; none are broken; and one has hatched!
I bet it won’t be long before there’s another Egg Score Card report with fresher news – so look for that! And I hope you’ll check back here as well; soon The Badger and the Whooping Crane will report on the eggs, nesting and hatching occurring among the Wisconsin whooping cranes out in the wilderness areas of our state.
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